Condition controlled reversible motor system

ABSTRACT

A condition controlled reversible motor system, disclosed as a temperature responsive system, operates to rebalance a bridge by means of a feedback potentiometer. The amplifier system connecting the bridge to the motor has a circuit means including a back biased diode that insures that the system always drives to a preferred or safe end in the event that the feedback potentiometer open-circuits or has a discontinuity between the wiper and the potentiometer resistor due to dirt or some other defect.

[ 1 May 1, 1973 United States ?atent 1 Pinckaers 3,548,271 12/1970 Kampfer........... 3,403,310 9/1968 Davidofi'.....

[54] CONDITION CONTROLLED REVERSIBLE MOTOR SYSTEM Primary ExaminerBenjamin Dobeck Attorney-Lamont B. Koontz et a1.

[57] ABSTRACT A condition controlled reversible motor system, dis- July 19, 1972 [21] Appl. No.: 273,245

closed as a temperature responsive system, operates to 318/295, 318/663 rebalance a bridge by means of a feedback poten- ...G05b l/06 .318/294, 295, 471,

[51] Int.

tiometer. The amplifier system connecting the bridge [58] held of to the motor has a circuit means including a back biased diode that insures that the system always drives to a preferred or safe end in the event that the feed- References cued back potentiometer open-circuits or has a discontinui- UNITED STATES PATENTS ty between the wiper and the potentiometer resistor due to dirt or some other defect.

3,323,031 Kasper et a1.......... ....318/295 X 3,405,336 Davidoff 6 Claims, 1 Drawing Figure PATENTED AY 1 191a I In CONDITION CONTROLLED REVERSIBLE MOTOR SYSTEM BACKGROUND OF THE INVENTION In condition controlled reversible motor systems using a feedback potentiometer, it is very desirable to provide some means to cause the motor system to drive to a preferred or safe position in the event that dirt or some other material builds up on the feedback poten- SUMMARY OF THE INVENTION The present invention is directed to a modification of a conventional bridge balanced motor drive system of a reversible nature which always provides a preferred or safe mode of operation in the event of an open-circuiting of the feedback potentiometer or its wiper. The disclosed system utilizes a dual operational amplifier and a bridge for providing the actuation of one or the other of the two amplifiers to cause the motor to operate in a correct direction to rebalance any unbalance in the bridge. The system further includes a connection between one of the amplifiers and one end of the rebalance potentiometer, including a diode, so that the diode is back biased in normal operation but provides a circuit to trigger the amplifier in a preferred manner in the event of an open-circuiting of the rebalance potentiometer or its wiper. With this arrangement, if the potentiometer open-circuits for any reason, the back bias is removed from the diode, and the diode connects the amplifier through the bridge to ground causing the amplifier to turn on to drive the motor in a predetermined, safe direction. In a heating system, this would normally mean that the heating system would be turned full on so that a building or occupied area would not freeze up in the winter time in the event of a motor feedback potentiometer failure.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the present application is a complete schematic diagram of a bridge operated reversible motor system utilizing dual operational amplifiers to control the motor in response to a condition responsive means.

DESCRIPTION OF THE PREFERRED EMBODIMENT A conventional alternating current line voltage source is connected between conductors 10 and 11 to a pair of terminals 12 and 13 that energize a transformer 14. The transformer 14 is a conventional step down type of control transformer having a low voltage secondary 15 that is connected to a diode 16 and to a conductor 17 that forms a ground or common for the system. The secondary winding 15 is also connected through a conductor 18 to a filter capacitor 20. The diode l6 and the filter capacitor 20 along with the secondary winding 15 provide a low voltage filtered direct current voltage source for the control system.

Conductor 18 is connected through a dropping resistor 21 to a conductor 22 that is connected by a zener diode 24 to the ground or conductor 17. The zener diode 24 provides a very accurately regulated voltage source between the conductors 22 and 17 for the remainder of the control system.

The control system utilizes a dual operational amplifier means 25 that has been disclosed schematically in a conventional fashion. The amplifier means 25 has sections designated as A and B. A non-inverting input for the A section is disclosed at 26, while the non-inverting input for the amplifier B is disclosed at 27. The inverting input for amplifier A is disclosed at 28, while the inverting input for amplifier B is disclosed at 30. The output of amplifier A is disclosed at 31 while the output of amplifier B is disclosed at 32. The dual operational amplifier means 25 can be of many commercially available types, and the present disclosure can be considered as utilizing an amplifier such as is commercially marketed by Fairchild- Semiconductor and which is known as the p.A739C. While the ptA739C is specifically mentioned, this is not intended in any way to limit the present invention to the utilization of this particular amplifier. The reference to this amplifier has been made merely as a convenience. The dual operational amplifier means 25 further has disclosed connections 33 and 34 which provide access to intermediate points in the amplifier configuration contained in the dual differential amplifier means 25. The terminal 33 is connected in the output section of amplifier B while terminal 34 is connected to an output section of amplifier A. Their specific functions in connection with the present invention will be described after the balance of the system has been disclosed.

The voltage source between conductors 22 and 17 supplies energy on conductors 35 and 36 to energize the dual operational amplifier 25, as well as a condition responsive voltage divider network means generally disclosed at 40. The condition responsive voltage divider network means 40 includes a rebalance potentiometer 41 made up of a potentiometer resistor 42 and a potentiometer wiper 43, with the potentiometer wiper 43 directly connected to the conductor 22. The condition responsive voltage divider network means 40 further includes a number of resistance elements that make up a bridge with its potential applied between the wiper 43 and the conductor 17. The left hand portion of the bridge includes'a part of thepotentiometer resistance 42, a fixed resistor 44, a setpoint potentiometer or resistor 45, and a pair of terminals 46 and 47 which are adapted to be connected to a resistance element 48, which in the present system is a negative temperature coefficient type of resistor and which forms a part of the condition responsive voltage divider network means 40.

The right hand portion of the condition responsive voltage divider network means 40 or the bridge includes a portion of the potentiometer resistor 42, a fixed resistor 50 in series with a further fixed resistance 51 and a group of calibration resistors 52, 53 and 54. The condition responsive voltage divider network means or bridge 40 further contains a fixed resistor 55 in parallel with the potentiometer resistor 42. A capacitor 56 for transient suppression and a pair of back to back diodes 57 and 58, which limit the signals to the dual operational amplifier means 25, are provided in a conventional fashion. I

The non-inverting terminal 26 of amplifier A is connected by conductor 60 to a further conductor 61 that connects back to the inverting terminal 30 of amplifier B. Conductors 60 and 61 have a common junction 62 which connect through a feedback resistor 63 to a conductor 64 which is connected to terminal 31 of the output of amplifier A.

The inverting terminal 28 of amplifier A is connected by conductor 65 to one side of the resistor 51 while the other side of resistor 51 is connected by conductor 66 to the terminal 27 or the non-inverting terminal of amplifier B. With the disclosed arrangement, the amplifiers A and B are controlled by a common input on I conductor 60 from one side of the bridge 40 and by a pair of slightly separated voltages created across the resistor 51 as supplied on the conductors 65 and 66 so that the two amplifier sections in the dual operational amplifier means 25 have a slight offset between their operating points and operate on reverse polarity signals. With the arrangement disclosed, when the bridge 40 is unbalanced so as to cause amplifier A to be active or conducting, the output on terminal 31 therefore suddenly rises to substantially the supply voltage on conductor 22. When the bridge is unbalanced in a reverse direction, the amplifier B becomes active and terminal 32 suddenly rises to a potential of approximately that of the conductor 22. Connected between conductor 66 and the output terminal 32 of amplifier B is a feedback resistor 67.

The output of the amplifier A at terminal 31 is connected by the conductor 64 and a conductor 70 to a transistor Q1 in a voltage divider arrangement across the capacitor 20. A similar arrangement is provided from terminal 32 and a conductor 71 to .a second transistor Q2 which is connected in a voltage dividing arrangement across the capacitor 20. Each of the transistors Q1 and Q2 controls current through their respective resistors 73 and 74 which in turn are connected by conductors 75 and 76 to a pair of triacs Q3 and Q4. The operation of the transistors 01 and Q2 are used to trigger selectively the triacs Q3 and Q4 depending on which of the dual operational amplifier means 25 has an output on terminal 31 or 32.

The triac Q3 is connected by a conductor 80, a limit switch 81 and a shading coil 82 to a reversible motor means generally disclosed at 84. The shading coil 82 is connected by a common conductor 85 to one side of the secondary of transformer 14. A second shading coil 86 is connected through a limit switch 87 and conductor 88 back to the triac Q4. The reversible motor means 84 is ofa well known type of shaded pole reversible motor and is commercially available from Honeywell Inc. and is known as the M934 type of motor. This disclosure is only one of many types of reversi ble motors that could be used in the present invention, and the reference is being supplied merely as a matter of convenience.

The reversible motor means 84 contains a rotor 90 and has a line voltage energize coil 91 to complete the electrical connection of the motor. The motor has an output shaft 92 that has mechanical linkages 93 and 94,

normally in the form of a cam operated arrangement, to operate the limit switches 81 and 87 to keep the rotation of the motor in a fixed number of rotational degrees. The rotor further has a mechanical connection shown at 95 to the wiper 43 of the feedback potentiometer. This wiper is used for a conventional closed loop rebalance typeof motor drive system.

The rotor 90 is adapted by a connection 96 to drive a load 97. The load 97 in the present disclosure, since the disclosure relates to a temperature responsive system, can be a damper or valve for the control of a heating or cooling medium to the system. The novel aspects of the present invention can be conveniently related to a heating system in which it is always desirable to have the system fail in a particular mode, which is called the safe mode. The failure mode that is safe for a heating system is for the heating system to be driven into a full heating condition. This prevents the accidental freezing up of equipment and plumbing in buildings, in which the system is installed, in case of a common component failure.

The system described to this point is a conventional condition responsive system operating a reversible motor for rebalance of a temperature sensitive bridge. in this type of a system one of the most common types of failures is for dirt or some foreign particle to accumulate on the wiper 43 of the potentiometer means 41. This tends to open the circuit to the bridge 40 and causes an unsafe type of failure. The opening of the wiper 43 from the potentiometer resistor 42 can also cause arcing which can cause the potentiometer resistor 42 to open-circuit. Either of these types of failures are undesirable and the present system provides a means for causing the system to always drive the motor in a preferred or safe direction. The arrangement forproviding this invention is in the connection of a diode 100 from an end 101 of the potentiometer resistor 42 through a resistor 102 to the terminal 33 in the dual operational amplifier means 25. The dual operational amplifier means 25 has an internal connection in which the terminal 33 connects to an amplifier stage which drives the amplifier B into full conduction if the terminal 33 is connected substantially to ground or conductor 17. In effect, the connection of the terminal 33 to ground 17 causes the output-transistor in amplifier B to conduct fully thereby connecting terminal 32 to the potential on conductor 22. This type of operation drives the transistor Q2 into full conduction which triggers the triac Q4 into conduction thereby fully energizing the motor 84 to operate in a selected direction.

Under normal operating conditions this is not possible since the conductor 22 feeds a potential through the wiper 43 to the potentiometer resistor 42 thereby providing a back bias across the diode 100. Under nor- 1 mal operating conditions, with the wiper 43 in contact with the potentiometer resistor 42, sufficient voltage is applied at the end 101 of the potentiometer resistor 42 to prevent any current from flowing through diode 100 tothe ground or conductor 17 through the bridge 40. If, however, the wiper 43 lifts from the potentiometer resistor 42 due to dirt, or if the potentiometer resistor 42 open circuits due to arcing, the circuit through diode 100 is completed and the amplifier B in the dual operational amplifier means 25 becomes fully operational to drive the system to a safe position.

In the present system a second circuit made up of a conductor 105, a resistor 106 and a diode 107 is provided back to the end 101 of the potentiometer resistor 42. In the event of a liftoff of the potentiometer wiper 43 or a discontinuity in the potentiometer resistor 42, current is drawn through terminal 34 of amplifier B through the resistor 106 and the diode 107 to the ground conductor 17. This biases off or grounds out amplifier A thereby operating along with the circuit means including diode 100 which has also become active to energize the output from amplifier B.

The inclusion of a circuit made up of the connection from terminal 34 through resistor 106 and diode 107 may or may not be used as an optional feature with the present invention. Basically the present invention is directed to a back biased circuit which causes the output to be actively energized in a particular direction. The additional control of amplifier A in a manner as to positively ground out its output insures that the amplifier A has no output which would attempt to control the triac Q3.

The present invention centers around the addition of a circuit means which connects one portion of the dual operating amplifier means to a bridge to provide a current path through the bridge to operate the amplifier in a particular manner in the event that the potentiometer means 41 fails to supply energy to the bridge 40, or has an open-circuit which removes power to a portion of the bridge. The normally back biased diode 100 guarantees that in the event of a loss of power at the end 101 of the potentiometer resistor 42, regardless of the reason, that the amplifier B if fully energized to drive the motor to one end of its rotation thereby opening the limit switch 87 and stopping the motor in a safe position in which full heat would be supplied in a heating system. The present invention is not limited to the specific motor nor amplifiers disclosed. The specific motor and amplifiers mentioned are by way of example only and the present invention is limited only by the scope of the appended claims.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A condition controlled reversible motor system with a safe mode of operation, including: voltage source and condition responsive voltage divider network means including rebalance potentiometer means operated by reversible motor means and adapted to be connected to condition responsive means as a part of said condition responsive voltage divider network means; dual operational amplifier means energized from said voltage source and selectively controlled by said condition responsive voltage divider network means to selectively control a pair of switch means; said switch means connected to control said reversible motor means so that the operation of a first of said switch means drives said motor means in a first direction while the operation of a second of said switch means operates said motor means in a reverse direction; said motor means operation normally occurring in response to a change in said condition responsive means to move said potentiometer means in such a manner as to rebalance said condition responsive voltage divider network to stop the operation of said motor means; and said dual operational amplifier means including further circuit means connecting said amplifier means to said voltage divider means to provide a current path through said voltage divider means to operate said amplifier means in the event that the continuity through said potentiometer means is disrupted thereby causing said amplifier means to operate said motor means to a safe position.

2. A condition controlled reversible motor system as described in claim 1 wherein said condition responsive voltage divider network means is a bridge.

3. A condition controlled reversible motor system as described in claim 2 wherein said rebalance potentiometer means includes a potentiometer resistance and a wiper with said voltage source connected between said wiper and another element in said bridge.

4. A condition controlled reversible motor system as described in claim 3 wherein said further circuit means connecting said amplifier means to said bridge is a circuit connected to an end of said potentiometer resistance and said amplifier means thereby causing said amplifier means to operate said motor means to said safe position in the event of a disruption of said voltage connection made normally through said wiper.

5. A condition controlled reversible motor system as described in claim 4 wherein'said circuit connected to said end of said potentiometer resistance includes a diode which is back biased when said potentiometer means is functioning normally in said bridge.

6. A condition controlled reversible motor system as described in claim 5 wherein said switch means are .solid state switches and said condition responsive 

1. A condition controlled reversible motor system with a safe mode of operation, including: voltage source and condition responsive voltage divider network means including rebalance potentiometer means operated by reversible motor means and adapted to be connected to condition responsive means as a part of said condition responsive voltage divider network means; dual operational amplifier means energized from said voltage source and selectively controlled by said condition responsive voltage divider network means to selectively control a pair of switch means; said switch means connected to control said reversible motor means so that the operation of a first of said switch means drives said motor means in a first direction while the operation of a second of said switch means operates said motor means in a reverse direction; said motor means operation normally occurring in response to a change in said condition responsive means to move said potentiometer means in such a manner as to rebalance said condition responsive voltage divider network to stop the operation of said motor means; and said dual operational amplifier means including further circuit means connecting said amplifier means to said voltage divider means to provide a current path through said voltage divider means to operate said amplifier means in the event that the continuity through said potentiometer means is disrupted thereby causing said amplifier means to operate said motor means to a safe position.
 2. A condition controlled reversible motor system as described in claim 1 wherein said condition responsive voltage divider network means is a bridge.
 3. A condition controlled reversible motor system as described in claim 2 wherein said rebalance potentiometer means includes a potentiometer resistance and a wiper with said voltage source connected between said wiper and another element in said bridge.
 4. A condition controlled reversible motor system as described in claim 3 wherein said further circuit means connecting said amplifier means to said bridge is a circuit connected to an end of said potentiometer resistance and said amplifier means thereby causing said amplifier means to operate said motor means to said safe position in the event of a disruption of said voltage connection made normally through said wiper.
 5. A condition controlled reversible motor system as described in claim 4 wherein said circuit connected to said end of said potentiometer resistance includes a diode which is back biased when said potentiometer means is functioning normally in said bridge.
 6. A condition controlled reversible motor system as described in claim 5 wherein said switch means are solid state switches and said condition responsive means is a temperature responsive resistance. 